Theories
Spontaneous Generation
Aristotle an early proponent
Life originating randomly from nonliving material
RNA World Hypothesis
In the primordial, pre-life world, early RNA could have catalyzed their own replication. Does not explain how RNA formed in the 1st place.
Suggested that individual organisms could change during their lifetimes by selectively using or not using various parts of their bodies. (ex: long neck in giraffe) He also suggested that individuals could pass these acquired traits on to their offspring. This is NOT supported by evidence
George Cuvier
Founded Paleontology. Found Elephant Fossils in Paris were different from elephants of Africa and other countries. Said must have been mass extinction events throughout time which were a result of periodic disasters
The Primordial Soup
Proposed in 1920’s by Alexander Oparin and John Haldane. Basic organic compounds formed from chemical “soup” eventually leading to evolution of life. Lightning sets off a chain of chemical reactions to form more complex organisms
Aliens
Maybe visitors from another planet brought microbes to early Earth??
Louis Pasteur
Disproved spontaneous generation with his swan-neck experiment (biogenesis). His experiments showed that life can only come from life.
Alexander Oparin & John Haldean
Proposed Primordial soup theory-basic organic compounds were formed in a chemical “soup” leading to evolution of life.
Life may have started next to hydrothermal vents
Dissolved Hydrogen, Nitrogen and Carbon became trapped and concentrated within the deep sea structures and other minerals and chemicals provided reaction catalysts that ultimately led to a similar process proposed by the primordial soup theory
Aristotle
One of the earliest recorded scholars on spontaneous generation (life coming from non-living material)
Miller & Urey
Tested the Oparin/Haldane primordial soup hypothesis by simulating Earth’s early atmosphere. Created organic molecules (life) from inorganic (nonliving)
Molded by clay
Clay as a scaffold (support) and helped to order the organic molecules (organic = life=carbon) into patterns. Eventually the molecules organize themselves. Still not widely accepted by science community
Said that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone. (competition for survival) Inspired Darwin’s ideas on natural selection
Alexander Graham Cairns-Smith
Organic Chemist who proposed the clay model. Clay minerals may have helped organized life’s molecules. Model not accepted by the scientific community
Eutectic Freeze-Thaw
Life originated in icy environments where freeze-thaw cycles could have concentrated organic compounds. Ice may have helped shield organic molecules from destruction by UV light and help concentrate them in bodies of water.
Hutten & Lyell
They concluded that the Earth is extremely old and that the processes that changed Earth in the past(like creating canyons from rivers) are the same processes that operate in the present and they occur over very long periods of time (gradualism)
Thomas Cech & Sidney Altman
Proved RNA can act as an enzyme catalyst (ribozymes)-Earned Nobel Prize in Chem. (previous thought was only proteins could act as catalysts) Support for the RNA World Hypothesis.